Cardiovascular adjustments and pain sensation usually occur when an organism encounters a "painful stimulus" associated with ischemia and infarction of the heart, but sometimes the insult does not produce pain (i.e. the "silent infarct"). The intermediate and long term objectives are to record activity of cells of origin of the spinoreticular tract (SRT) and the medial and lateral spinothalamic tract (STT) system, of the thalamus, and of the somatosensory cortex and examine the complex interactions that occur between the cardiovascular system, particularly the heart, and the pain system. The working hypothesis of this proposal is that activation of vagal afferent fibers stimulates brainstem structures whose projections descend to modulate the activity of SRT and STT neurons in the Tl-T5 segments of the spinal cord. The upper thoracic spinal cord of cats (SRT cells) and monkey (STT cells) will be explored with carbon filament or tungsten microelectrodes to record single extracellular action potentials of cells antidromically activated from the thalamus or the medullary reticular formation. The specific aims are to: 1) determine effects of electrically, mechanically or chemically stimulating vagal afferent fibers on activity of SRT and STT cells responding to visceral and somatic inputs; 2) determine nuclei and descending pathways activated during vagal stimulation by applying focal electrical and chemical stimulation and by making lesions; 3) simultaneously record activity of raphe-spinal and STT and SRT cells during vagal stimulation; and 4) examine the effects of independently occluding branches of the left coronary artery and the right coronary artery on the activity of STT or SRT cells before and after vagal cooling or vagal stimulation. This study will contribute to understanding the interactions of neural mechanisms that underlie cardiac pain, the associated angina pectoris and possibly the "silent infarction."